Method of and means for producing oscillations



Jan. 5, 1937. TZ 2,066,902

'METHOD- OFAND MEANS FOR PRODUCING OSCILLATIONS Filed May 24, 1934 2Sheets-Sheet l M I Z040 0M0 (mm r sax/ea 0/050 (WERE/W.

sou/9c! INVENTOR JOHN L. REINARTZ ATTORNEY Jan, 5, 1937.

J.- L. REINARTZ 02 METHOD OF AND MEANS FOR PRODUCING OSCILLATIONS- FiledMay 24, 1934 "2 Sheets-Sheet 2 a/kicr cue/e50 2. 5? 5 F@\ f 14 1 K rINVENTOR JOHN R EINARTZ BY gwl/ v ATTORNEY Patented Jan. 5, 1937 UNITEDSTATES PATENT OFFICE John L. Reinartz, Manchester, 001111., assignor toRadio Corporation of America, a corporation 7 of Delaware ApplicationMay 24, 1934, Serial No. 727,215

2 Claims.

This invention relates to a method of and means for producingoscillations of constant frequency and, if desired, multiplying thefrequency of the oscillations so produced. More in detail 5 the presentinvention relates to a method of and circuit arrangements for utilizingefficiently thermionic tubes of the multi-electrode type heretoforecommonly used in class B operation, in class C operation as oscillationgenerators, amplifiers and/or frequency multipliers. In general, thetubes involved are of the type comprising a cathode, a control grid, oneor more additional grid-like electrodes and an anode.

Class B tube operationis characterized by the condition that arelatively low plate current is maintained when no excitation issupplied to the control grid of the tube. When a signal of sufficientmagnitude is applied to the grid, there will be no plate current flowover a substantial part of the negative cycle of said signal. Current,

however, .will flow during the positive or less negative portion of thecycle of said signal. Ideal class B operation is attained when thealternating component of plate current is an exact replica of the inputsignal for the half-cycle when the grid is positive and the platecurrent flows during 180 electrical degrees of the applied signal.

Tubes of the type described above when used in class B operationgenerally have their grids connected directly together and to thecathode by Way of the input impedance. No biasing potential source isnecessary, the tubes in operation relying on the potential produced bygrid rectification of the signal wave in the grid circuit.

Tubes of the type described above have also been used in class Aoperation. When so used, the control grid is excited by the wave to beamplified. The auxiliary grid electrode is connected directly to theanode electrode so that in effect we. have a triode. In some instanceswhen these tubes are used as class A amplifiers the screen gridelectrode being nearer to the cathode draws exceedingly heavy currentand is destroyed.

This defect, of course, would not hold where the additional gridelectrode is tied to the control grid.

With class C operation of the tube the bias applied to the gridelectrode is appreciably more than necessary to cut oil the platecurrent to zero when no exciting voltage is applied to the control grid,so that the plate current flows in the tube for appreciably less thanone-half of each cycle. In this case jabs of current appear in the anodecircuit during much less than degrees of the applied wave. Class Coperation is attained with extremely high plate circuit efliciency.

An object of the present invention is to provide 5 a new method of andcircuit arrangement for operating thermionic tubes of the classdescribed above as oscillation generators and operating said tubes insaid circuit as class C relays.

Another object of the present invention is to 10 provide a method ofand. circuit arrangements for producing high frequency oscillations in athermionic tube of the multi-grid type and for impressing saidoscillations on an output circuit which is coupled to the generatingcircuits by 15 the electron stream only of the tube. In this circuit,changes or variations in the load coupled to the output circuit have noeffect whatever on the constants of the frequency generating anddetermining circuits. 20

Another object of the present invention is to provide an oscillationgenerator utilizing a multigrid electrode of the type described in whichthe control grid, cathode and one or more grid-like electrodes make up aconventional triode in which 25 oscillations may be generated of afrequency determined by the constants of the circuits connecting saidelectrodes or by an additional frequency determining element and inwhich an output circuit electro-magnetically separated from, 30 butelectronically coupled to the prior electrodes and circuits may beconnected between the anode and cathode of the tube.

Another object of the present invention is to provide a circuitarrangement as described in 35 the preceding paragraph in which thecircuit be tween the anode and cathode of the tube may be tuned to thefundamental frequency generated in the triode operation of the tube orto a multiple of said frequency. 40

When exceptional stability is desired in the circuit briefly describedin the two preceding paragraphs, the anode electrode and circuit may befurther dissociated from the triode portion of the tube and the circuitsthereof by connecting 45 neutralizing condensers between the desiredelectrodes in the triode portion of the tube and the anode.

In the triode portion of the tube sustained oscillation may be assuredby connecting coupling 5 condensers between the control grid andgrid-like electrodes of the tube to produce a feed back of energy fromthe grid-like electrode adjacent the anode to the control gridelectrode. In a pushpull arrangement the control grids of each tube 55may be fed energy from the grid-like electrode of the other tube.

Numerous otherobjects of the present invention and advantages derivedfrom the use thereof will become apparent from the following detaileddescription thereof when read in connection with the attached drawingsthroughout which like reference symbols indicate like parts insofar aspossible and in which,

Figure 1 shows, for purposes of illustration only, an oscillationgenerator circuit in which tubes of the type described above areconnected in a novel manner to produce oscillations of substantiallyconstant frequency and to apply the same to a load circuit in such amanner that variations of said load have no effect on the constancy ofthe frequency producing circuits.

Figure 2 shows a modification of the arrangement of Figure 1.

Figure 3 shows an oscillation generator including thermionic tubes ofthe multi-grid electrode type in which certain electrodes of the tubeare connected for triode oscillation generation,

while other electrodes are connected in an output circuit coupled onlyby the electron stream of the tube to the prior circuits; while,

I Figure 4 shows a modification of the arrangement of Figure 3.

Referring to Figure 1, A and B are a pair of thermionic tubes havingcathodes K, control grids I and I 2 and anodes 3 and 3. The grids 2 and2 are connected as shown in pushpull relation by a circuit IE comprisingan inductance L and a tuning capacitor C. Grid I of tube A is connectedas shown by way of a feedback capacitor FB to grid 2' of tube B, whilegrid I of tube B is connected as shown by way of a feedback capacitor FBto grid 2 of tube A. The circuit I 0 is tuned to the frequency it isdesired to generate and is preferably preponderantly inductive incharacter. Due in part to the impedance of this circuit and in part tothe feed back supplied by the condensers FB sustained oscillations ofthe desired frequency are developed in the circuit I0 and the electrodesI, 2, I and 2.

A circuit 20 comprising an inductance M and tuning capacitor D isconnected as shown between the anodes 3 and 3 of the tubes A and B. Thiscircuit 20 may be coupled in any manner to any load showndiagrammatically at 24. The oscillations produced in the circuit I 0 areimpressed by way of the electron stream in the tubes A and B to thecircuit 20 which is magnetically isolated with respect to the circuitIt]. The control grids of the tubes derive their biasing potentials byway of resistances R connected as shown between said control grids andthe cathodes. No separate biasing potential source is necessary. Theanodes and grid-like electrodes of the tubes derive their positivepotential from a direct current source connected as shown to pointsintermediate the terminals of inductances L and M respectively.

In actual practice it was found that a considerable change of the loadon the anodes of the tube resulted in no change in the frequencygenerated and in the amount of direct current flowing in the controlgrid circuits. Moreover this is true whether the circuit DM be tuned tothe fundamental frequency to which LC is tuned or to a multiplefrequency in.

In the arrangement of Figure 2 a single tube A has its control grid Iconnected as shown by way of a resistance R to its cathode K. A freandauxiliary grid electrodes 2 and quency determining piezo-electriccrystal PC is connected as shown between grid I and the oathode. Thegrid-like electrode 2 of this tube is connected by way of a circuit LCto the cathode of the tube. This electrode 2 serves as the anode of atriode system in which oscillations are produced of a frequencydetermined by the crystal PC. In this arrangement the circuit LC ispreferably tuned to a frequency slightly above the frequency of thecrystal so as to increase the impedance of this circuit and therebyinsure the production of sustained oscillations in the tube. The anode 3is connected as shown by way of an output circuit 20 to the cathode ofthe tube. Here, as in the prior case, the anode is coupled to thefrequency determining circuits only by way of the electron stream of thetube. The cir' cuit 20 is electro-magnetically isolated from the othercircuits of the tube. To further insure decoupling between the differentelements including the anode electrode 3, and its circuit 20, the screengrid 2 and the frequency determining circuit CL a neutralizing capacitorNC is connected as shown between the anode 3 and the grid 2 by way ofthe circuit CL. It will be noted here that by using this tube inapplicants novel circuit results are obtained equivalent to the use oftwo tubes. The tube first serves as an oscillation generator and then asan amplifier in case the circuit 26 is tuned to the fundamentalfrequency or as a frequency multiplier in case the circuit 20 is tunedto a harmonic fn.

In operation oscillations are produced in the circuits connected withelectrodes K, I and 2 of a frequency determined in part by thepiezoelectric crystal PC. These oscillations appear in the circuit CLfrom which they may be utilized if desired. However, it is preferable toplace no load on the circuit CL and to derive the useful oscillationsfrom the circuit 20. This insures a more constant operation in thetriode portion of the tube.

In order to eliminate to a great extent the harmonies which may bepresent in the tank circuit 20 of the device of Figure 2, I make use ofa pushpull arrangement as shown in Figure 3. The thermionic tubes A andB have their control grids I and I connected as shown by way ofresistances R to their cathodes K. A frequency determiningpiezo-electric crystal PC is connected between the control gridelectrodes I and I. The grids 2 and 2' of the tubes A and B areconnected as shown in pushpull relation by a frequency determiningcircuit CL which may be tuned to substantially the frequency of thecrystal PC. A positive potential is applied between grids 2 and 2 andthe cathode by connecting the positive terminal of a source to a pointon the inductance L and the negative terminal of the source to thecathodes of the tubes A and B. The electrode system, which is similar toa triode, and circuits so far described when energized produce sustainedoscillations of constant frequency. The anodes 3 and 3' of the tubes Aand B are connected in push-pull by tuned tank circuit 20 as shown. Thepositive terminal of the direct current source is connected to a pointon the inductance M. A load circuit may be coupled to the inductance M.The oscillations produced in the triode portion of the tubes andappearing in CL are transferred by way of the electron stream only ofthe tubes A and B to the anodes 3 and 3, and from the anodes to the tankcircuit 20. The oscillations in the tank circuit 20 may be impressed onthe load circuit. The tank circuits 20 may be tuned to 75 thefundamental frequency, that is, to the frequency of the crystal PC or toa harmonic thereof. Due to the pushpull arrangement many of theharmonics which might be present in the arrangement shown in Figure 2will not be present in the circuits of Figure 3. To further insure thatthere is no coupling between the output circuit 20 and anodes 3 and 3other than by way of the electron stream in the tubes neutralizingcapacitors CN may be connected as shown between the anode of the tube Aand grid 2 of tube B and between the anode of tube B and grid 2 of tubeA. In operation it was found that there was no reaction whatever presenton the grids 2 and 2' when the tank circuit is tuned through resonance.The generator operated in a stable manner to produce oscillations of aconstant frequency and to amplify or frequency multiply the same.Moreover, it was possible to key the plate circuit of the generator withno appreciable change in the frequency as determined by the triodesystem including CL and a. piezo-electric crystal PC.

In some cases it is not desirable or not practical to use piezo-electriccrystals in the circuits. 1 have provided a novel circuit by means ofwhich sustained oscillations of substantially constant frequency may beobtained without the use of a frequency determining element such as apiezoelectric crystal. Such a circuit has been shown in Figure 4 whereinthe electrodes of the tubes have been spaced out to show more clearlythe separation between the various circuits and the circuitarrangements.

The grid electrodes l and l of tubes A and B are connected as shown tothe cathodes K by way of biasing resistances R. The grids 2 and 2 oftubes A and B are connected as shown in pushpull relation by a tunedtank circuit CL. This circuit is tuned to the frequency of theoscillations it is desired to generate and determines said frequency.Positive potential is supplied to the electrodes 2 and 2' by way of aconnection between a point at the electrical center at L and thepositive terminal of a direct current source, the negative terminal ofwhich is connected to the cathodes K. The grid electrode 2' of tube Bwhichis serving as the anode of a triode system is connected by way of afeed back condenser FB to the electrode l of tube A. The electrode 2 oftube A, which is acting as an anode of a second triode system isconnected by way of a feed back condenser FB to the grid l of the tubeB. When the circuits are arranged as shown and energized as shown thegrids 2 and 2' serve as the anodes of a triode system in which sustainedoscillations are produced of a frequency determined by CL. The anodes 3of tubes A and B are connected as shown in pushpull relation by a tankcircu't 20. The positive potential for the anodes 3 is supplied by wayof a connection between the electrical center of M and the positiveterminal of the direct current source. The sustained oscillationsproduced in the triode system and appearing in the circuits CL areimpressed by way of the electron stream to the anodes 3 and from 3 tothe tank circuit 20. The tank circuit 20 may betuned to the fundamentalfrequency F or to the harmonic FM. The oscillations may be applied fromN to any load circuit 24. Here again changes in the load circuit or inthe tuning of the tank circuit 20 cause little or no effect on thefrequency generated in the triode portion of the tube. Moreover changesin load or in tuning of the tank circuit can be prevented entirely fromaffecting the frequency of the oscillations produced if the anode ofeach tube is connected as shown by way of neutralizing condensers CM tothe grids 2 and 2' of the other tube.

A separate source of direct current is shown connected between a pointon the inductance L connected with the grids 2 and 2'. When using a highcapacity circuit CL connected with grids 2 and 2' and when this tankcircuit CL is supplied from a separate direct current source whichcannot change when the anode circuit 20 is keyed, then there is nochange in the current drain in the circuit connected or no change in thefrequency produced in the triode portion and radiated from 20.

It will be noted that in all of these electron coupled oscillatorsand/or frequency multipliers, no grid biasing potential source isutilized. Moreover, in each of the circuits shown the oathodes of theelectron coupled oscillator tubes are maintained at ground radiofrequency potential. This is of considerable importance because it lendsto stability of operation and helps to insure production of oscillationsof constant frequency. Moreover, from a practical standpoint, as will bereadily understood, it is of advantage to have the cathode which isheated by low fre-.

quency or direct current at ground radio frequency potential. If thecathode must be operated at high radio frequency potential, as is thecase in electron coupled oscillators known heretofore, considerableprecautions and added expense are involved in insulating or raising thecathode and its heating circuits and sources above ground potential.

Having thus described my invention and the operation thereof, what Iclaim is:

1. An oscillation generator of the push-pull type comprising a pair ofelectron discharge tubes each having a cathode, an anode, and at leasttwo grid electrodes, including a control grid and a screen grid, a tankcircuit interconnecting the two anodes, a second tank circuitinterconnecting the screen grid electrodes, an input circuit for eachtube disposed between the oathode and the control grid thereof, eachsaid input circuit comprising means for maintaining a negative bias onsaid control grid with respect to the cathode of such value that lessthan 180 of each cycle of an applied excitation wave is available torender the tube conductive, two symmetrically disposed feed-backcapacitors each intercoupling the control grid of one tube with thescreen grid of the other tube, means including a direct current sourcefor so polarizing said electrodes each with respect to the other as toactivate said tubes, and means including two symmetrically disposedcapacitors each intercoupling the screen grid of one tube with the anodeof the other tube for neutralizing the inter-electrode capacitances ofsaid tubes. 7

2. An oscillation generator according to claim 1 and furthercharacterized in that the two said tank circuits are so tuned that theresonant frequency characteristics thereof bear a harmonic relationship,one to the other.

JOHN L. REINARTZ.

